Low noise and low voltage mixer and intermediate frequency module application thereof

ABSTRACT

A mixer includes a reference current source, a programmable gain RF transconductance section or an RF transconductance section, switching quad native transistors or switching quad transistors, and a folded-cascoded common mode output section or an output section. When the mixer included the programmable gain RF transconductance section, the gain of the mixer is adjustable. When the mixer includes the switching quad native transistors, flicker noise of the mixer is reduced. When the mixer includes the folded-cascoded common mode output section, the mixer operates reliably from low supply voltages.

This patent application is claiming priority under 35 USC § 120 as acontinuing patent application of co-pending patent application entitledMIXER HAVING LOW NOISE, CONTROLLABLE GAIN, AND/OR LOW SUPPLY VOLTAGEOPERATION, having a filing date of Jan. 7, 2002, and a Ser. No.10/041,148.

TECHNICAL FIELD OF THE INVENTION

This invention relates generally to radio frequency (RF) technologiesand more particularly to mixers used within such RF technologies.

BACKGROUND OF THE INVENTION

Wireless communication systems are known to enable one wirelesscommunication device to transmit data to at least one other wirelesscommunication device via a wireless transmission medium. Such wirelesscommunication systems may range from National or International cellulartelephone systems to point-to-point in-home networking. For instance, awireless communication system may be constructed, and hence operates, inaccordance with one or more standards including, but not limited to,IEEE 802.11a, IEEE 802.11b, Bluetooth, advanced mobile phone services(AMPS), digital AMPS, global system for mobile communications (GSM),code division multiple access (CDMA), wireless application protocol(WAP), local multi-point distribution services (LMDS), multi-channelmulti-point distribution systems (MMDS), and/or variations thereof.

As is also known, such wireless communication systems use radiofrequencies for the wireless transmission medium. Thus, each wirelesscommunication device that transmits data requires an RF transmitter andeach wireless communication device that receives data requires an RFreceiver. In general, an RF transmitter includes a modulator, localoscillator, one or mixers, power amplifier and an antenna. Theinter-operation of these components is well known to modulate a datasignal into an RF signal. Correspondingly, an RF receiver includes anantenna, which may be shared with the RF transmitter, a low noiseamplifier, a local oscillator, one or more mixers, a summing module,filtering, and a demodulator to recapture the data signal from the RFsignal.

Consequently, each wireless communication device includes a plurality ofmixers within the RF transmitter and RF receiver to properly functionwithin any type of wireless communication system. Not surprisingly, thequality of performance of a wireless communication device is dependenton the quality of performance (e.g., linearity) of the mixers includedtherein. A high quality mixer for certain applications is illustrated inFIG. 1 and is known as the Gilbert mixer. The Gilbert mixer, as shown,may be implemented using standard CMOS technology, however, for lowsupply voltage applications (e.g., less than 3.3 volts), it is difficultto obtain sufficient gain due to the output resistors R0 and R1.

To overcome this limitation, the Gilbert mixer can be modified as shownin FIG. 2. While this configuration improves the headroom capabilitiesof the mixer, it still has some limitations. For instance, such a mixerlacks built-in gain control, which would allow the gain of the mixer tobe adjusted for various applications. In addition, the mixer, when usedto directly translate RF signals into base-band signals, includes asignificant amount of flicker noise, which is produced by switchingtransistors MG1-MG4. Further, the voltage excursion on switchingtransistors MG1-MG4 may be quite large, which causes device reliabilityissues of the switching transistors. Still further, the maximum swing ofthe mixer output, while maintaining acceptable distortion performance,could be quite limited for low supply voltage applications (e.g., lessthan 2 volts).

Therefore, a need exists for a mixer that reliably operates at lowvoltages (e.g., less than 2 volts), provides gain adjustments, reducesadverse affects of flicker-noise and/or limits voltage excursions of itsswitching transistors, which improves device reliability.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a schematic block diagram of a prior art mixer;

FIG. 2 illustrates a schematic block diagram of an alternate prior artmixer;

FIG. 3 illustrates a schematic block diagram of a mixer in accordancewith the present invention;

FIG. 4 illustrates a schematic block diagram of an alternate mixer inaccordance with the present invention;

FIG. 5 illustrates a schematic block diagram of another mixer inaccordance with the present invention;

FIG. 6 illustrates a schematic block diagram of a further mixer inaccordance with the present invention;

FIG. 7 illustrates a schematic block diagram of a still further mixer inaccordance with the present invention;

FIG. 8 illustrates a schematic block diagram of a programmable gain RFtransconductance section that may be incorporated in one or more of themixers of FIGS. 3 through 7;

FIG. 9 illustrates a schematic block diagram of an alternateprogrammable gain RF transconductance section that may be incorporatedin one or more of the mixers of FIGS. 3 through 7;

FIG. 10 illustrates a schematic block diagram of yet another mixer inaccordance with the present invention;

FIG. 11 illustrates a schematic block diagram of yet a further mixer inaccordance with the present invention;

FIG. 12 illustrates yet another embodiment of a mixer in accordance withthe present invention; and

FIG. 13 illustrates a schematic block diagram of an intermediatefrequency module in accordance with the present invention.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT

FIG. 3 illustrates a schematic block diagram of a mixer 10 that includesa reference current source 12, a programmable gain RF transconductancesection 14, and switching quad transistors 16. The reference currentsource 12 is operably coupled to provide a reference current 28 to theprogrammable gain RF transconductance section 14. The programmable gainRF transconductance section 14, which will be described in greaterdetail with reference to FIGS. 8 and 9, receives a RF signal 18 and again setting signal 22. Based on these inputs and the reference current28, the programmable gain RF transconductance section 14 produces an RFcurrent 24. Accordingly, the RF current 24 is representative of the RFsignal 18 amplified in accordance with the gain setting signal 22.

The switching quad transistors 16 are operably coupled to generate afrequency translated current 26 from a local oscillation voltage 20 andthe RF current 24. Accordingly, the frequency translated current 26represents an up-conversion of the RF current 24 with respect to thelocal oscillation voltage 20 and a down-conversion of the RF current 24with respect to the local oscillation voltage 20. For example, if the RFcurrent 24 is represented by sin (ω_(RF)t) and the local oscillationvoltage 20 is represented by sin (ω_(L0)t), the frequency translatedcurrent 26 would essentially equal ½ cos (ω_(RF)−ω_(L))t−½ cos(ω_(RF)+ω_(L))t. Accordingly, the cosine component including thedifferences between the frequency represents the down-conversion and thecosine portion including the summation of the frequencies represent theup-conversion.

The switching quad transistors 16 may be implemented utilizing nativetransistors or non-native transistors. Such non-native transistors havea gate-to-source voltage threshold that is greater than 0 volts and istypically in the range of 0.4 volts to 0.7 volts. A native transistorhas a gate to source voltage threshold of approximately 0 volts. Byutilizing the native transistors, which have a larger minimum channellength than non-native transistors, within the switching quad transistor16, flicker-noise is reduced in comparison to using non-nativetransistors. In addition, by utilizing native devices within theswitching quad transistors, the maximum voltage experienced by the gatebody junction of the switching quad transistors is reduced by almost 1voltage threshold. Accordingly, this helps the reliability of theswitching devices.

FIG. 4 illustrates a mixer 30 that includes the reference current source12, the programmable gain RF transconductance section 14, the switchingquad transistors 16, a resistor section 36, a current source pair 34,and a common mode circuit 32. In this configuration, the switching quadtransistor 16, the programmable gain RF transconductance section 14, andthe reference current source 12 operate as previously discussed withreference to FIG. 3.

The current source pair 34 is operably coupled to provide a DC current38 to the switching quad transistors. The resistor section 36 isoperably coupled to provide a current-to-voltage translation and toprovide a common mode reference for common mode circuit 32. The commonmode circuit 32 provides a gate voltage to the current source A pair 34to regulate the DC current 38 at a desired level.

In this implementation, mixer 30 provides a mixed voltage output ofIF_(n) and IF_(p), which results from the current-to-voltage translationprovided by the resistor section 36. Also, in this configuration, themixer provides a low noise and gain controllable mixer that can operateat low voltage supplies (e.g., approximately 2 volts).

FIG. 5 illustrates a schematic block diagram of a mixer 40 that includesthe reference current source 12, the programmable gain RFtransconductance section 14, the switching quad transistor 16 and aresistor section 42. In this configuration, the frequency translatedcurrent 26 is directly converted to a voltage via the resistor section42.

As one of average skill in the art will appreciate, the mixer 40 of FIG.5 provides controllable gain and low noise operation, especially whenthe switching quad transistors are implemented utilizing nativetransistors. However, in comparison with the mixer of FIG. 4, mixer 40requires a slightly larger operating voltage.

FIG. 6 illustrates a mixer 50 that includes reference current source 12,the programmable gain RF transconductance section 14, the switching quadtransistors 16, current source pair 34, a common mode circuit 52, and abias circuit 54. The bias circuit 54 is operably coupled to the currentsource pair 34 to provide gate voltage to the current source pairenabling it to produce the DC current 38.

The common mode circuit 52 includes a resistor divider 58, anoperational amplifier 56, transistor pair 60, and resistor pair 62. Theresistor divider 58 is operably coupled to the switching quadtransistors 16. The tap of the resistor divider 58 provides a commonmode reference to the operational amplifier 56. The other input of theoperational amplifier is coupled to a reference voltage. Accordingly,the common mode circuit 52 will regulate the common mode of thefrequency translated current 26 with respect to the reference voltageprovided to the input of the operational amplifier 56. The operationalamplifier 56 drives the transistor pair 60 to produce a current that isprovided to the resistor pair 62. The interconnection between thetransistor pair 60 and resistor pair 62 provides the mixer output 64.

As one of average skill in the art will appreciate, by utilizing thecommon mode circuit 52 in conjunction with the other componentsillustrated in FIG. 6, the supply voltage may be further decreased thusallowing mixer 50 to have a high quality of performance at very lowsupply voltages (e.g., approximately 1 volt to 1.8 volts). As one ofaverage skill in the art will further appreciate, the common modecircuit 52 provides a folded cascoded output, which reduces voltageexcursions of the transistor pair 60 thereby significantly improvingsupply voltage headroom at the mixer output 64. As one of average skillin the art will still further appreciate, the common mode voltage of thefrequency translated current 26 is now an intermediate node within themixer, hence the common mode of the frequency translated current 26 iscontrolled, which reduces voltage swings on the drain side of thetransistor pair 60. This further improves lower voltage operation of themixer. As one of average skill in the art will also appreciate, theprogrammable gain RF transconductance section 14 allows the mixer tohave controllable gain while the switching quad transistor 16,especially when implemented with native transistors, reduces noise ofthe mixer.

FIG. 7 illustrates another mixer 70 that includes the reference currentsource 12, the programmable gain RF transconductance section 14, theswitching quad transistor 16, the bias circuit 54, the current sourcepair 34, and a common mode circuit 72. The operation of the bias circuit54, the current source pair 34, the switching quad transistor 16, theprogrammable gain RF transconductance section 14 and the referencecurrent source 12 are as previously discussed.

The common mode circuit 72 includes the resistor divider 58, transistorpair 60 and resistor pair 62 of the common mode circuit 52 of FIG. 6.The common mode circuit 72 further includes a 2^(nd) resistor dividerthat includes resistors 74 and 76. The 2^(nd) resistor divider 74 and 76allow the reference voltage into operational amplifier 56 to be reduced.By reducing the reference voltage, the operational amplifier 56 has itsoutput range at approximately {fraction (7/10)}ths of a volt. Thisenables the operational amplifier to be implemented utilizing a singlestage N-input or P-input operational amplifier and meet the constringentheadroom constraints. Accordingly, the reference voltage may be set toapproximately 900 milivolts.

FIG. 8 illustrates a schematic block diagram of an embodiment of theprogrammable gain RF transconductance section 14 that includes a RFinput transistor pair 82, a 1^(st) inductor L1, a 2^(nd) inductor L2,and a selectable transistor section 80. As shown, the RF inputtransistor pair 82 includes a pair of N-channel transistors operablycoupled to receive the RF signal 18. The inductors L1 and L2 eachinclude a tap that is operably coupled to the selectable transistorsection 80. The selectable transistor section 80 includes threeN-channel transistors.

The gain setting signal 22 is coupled to the gates of the transistors ofthe selectable transistor section 80. When the gain setting signal 22 isin a low-gain state, the center transistor, which is coupled to the nodecoupling L1 and L2, is active while the other two transistors areinactive. As such, the reference current 28 is based on thetransconductance produced via the RF input transistor pair 82 and thefull inductance of inductors L1 and L2.

When the gain setting signal is in a high-gain state, the outsidetransistors of the selectable transistor section 80 are enabled. Thiscouples the taps of inductors L1 and L2 to produce the reference current28. As such, the gain of the transconductance section 14 is increasedsince the inductance provided by L1 and L2 is reduced in comparison thelow-gain state operation.

FIG. 9 illustrates a schematic block diagram of an alternate embodimentof the programmable gain RF transconductance section 14. Thetransconductance section 14 includes the RF input transistor pair 82, adifferential tapped inductor L3 and the selectable transistor section80. The functionality of the RF input transistor pair 82 and theselectable transistor section 80 are as previously discussed withreference to FIG. 8.

The differential tapped inductor L3 is a differential inductor that haseach section tapped as illustrated. Accordingly, when the gain settingsignal 22 is in a low-gain state, the center transistor of theselectable transistor section 80 is activated thus, employing the fullinductance of both sections of the differential tapped inductor. Whenthe gain setting signal 22 is in a high-gain state, the outsidetransistors of the selectable transistor section 80 are active thus,only a portion of the inductance of L3 is utilized.

As one of average skill in the art will appreciate, resistor dividersmay be used within the transconductance section instead of the inductorsto provide selectable gain, additional inductors may be used to providefurther granularity of gain settings, or a combination thereof may beutilized. Regardless of the specific implementation used, thetransconductance section 14 may be programmed to adjust the gain of themixer for various mixing applications thus, enhancing the performance ofsuch a mixer over a wide range of mixing applications.

FIG. 10 illustrates a schematic block diagram of mixer 90 that includesswitching quad native transistors 92, a RF transconductance section 94,.and a reference current source 12. As configured, the reference currentsource 12 produces a reference current 28 that is provided to the RFtransconductance section 94. The RF transconductance section 94generates a RF current 24 from a RF signal 18 based on the referencecurrent 28.

The switching quad native transistors 92, which each include nativetransistors, convert the RF current 24 into a frequency translatedcurrent 26 based on a local oscillation voltage 20. The nativetransistors utilized within the switching quad native transistors 92reduce the flicker-noise injected by the mixer thereby increasing theperformance capabilities of such a mixer.

FIG. 11 illustrates a mixer 100 that includes the current source pair34, common mode circuits 52 or 72, the switching quad native transistors92, the RF transconductance section 94, and the reference current source12. The RF transconductance section 94 includes a pair of transistorsoperably coupled to receive the RF signal 18 and a pair of inductors.The inductors improve the linearity of the RF transconductance section94 but reduce the gain of the mixer. Alternatively, resistors mayreplace the inductors when headroom of the supply voltage is a lesscritical issue.

The overall function of mixer 100 is in accordance with the functioningof the mixers previously described. In particular, the RFtransconductance section 94 converts an RF signal 18 into an RF current26. The switching quad native transistors 92 convert the RF current intoa frequency translated current 26 based on a local oscillation voltage20. The common mode circuit 52 or 72 provides a common mode referencepoint to produce the mixer output 64. To facilitate the generation ofthe frequency translated current 26; the current source pair 34 providesa DC current 38. Alternatively, resistors may replace the current sourcepair 34 if headroom of the supply voltage is a less critical issue.

FIG. 12 illustrates a schematic block diagram of yet another mixer 110that includes the reference current source 12, the RF transconductancesection 94, switching quad transistor 16, common mode circuits 52 or 72and current source pair 34. The functionality of mixer 110 is similar tothe functionality of mixer 100 except that the switching quad nativetransistors 92 of mixer 100 have been replaced with non-nativetransistors within switching quad transistors 16.

FIG. 13 illustrates a schematic block diagram of an intermediatefrequency module 120 that includes a 1^(st) mixer 124, a 2^(nd) mixer126, a local oscillator 122, a summing module 128 and a filter module130. The IF module 120 may be used in a radio frequency receiver and/orin a radio frequency transmitter.

In operation, the 1^(st) mixer 24 receives an in-phase component of aninput signal 32 (e.g., an RF signal for a receive and an IF signal for atransmitter) and an in-phase component of local oscillation voltage 20.The 1^(st) mixer 124, which may be any of the mixers illustrated inFIGS. 3-12, mixes the in-phase input signal and in-phase localoscillation to produce an I product 134. Similarly, the 2^(nd) mixer 126mixes a quadrature portion of the input signal 132 with a quadraturecomponent of the local oscillation voltage 20 to produce a quadratureproduct 136. Each of the I and Q products 134 and 136 will include anup-conversion of the input signal based on the local A oscillationvoltage 20 and a down-conversion of the input signal based on the localoscillation voltage 20.

The summing module 128 sums the I product 134 and the Q product 136 toproduce a summed signal 138. The filtering module 130 filters either theup-converted portion of the summed signal 138 or the down-conversionportion of the summed signal 138 to produce an IF signal 140. Thefiltering module 130 will filter the down-conversion portion of thesummed signal 138 such that the up-conversion portion is left when theIF module 120 is incorporated in a radio transmitter. Conversely, thefiltering module 130 will filter the up-conversion portion of the summedsignal 138 and thus pass the down-conversion portion of the summedsignal 138 when the IF module 120 is incorporated in a radio receiver.

The preceding discussion has presented a mixer that providesprogrammable gain, reduces flicker-noise, and/or operates from smallsupply voltages. By employing the programmable gain RF transconductancesection, a mixer includes programmable gain; by utilizing nativetransistors within the switching quad transistors, flicker-noise isreduced; and by utilizing a folded-cascoded common mode circuit, voltageoperations may be reduced. As one of average skill in the art willappreciate, other embodiments may be derived from the teachings of thepresent invention without deviating from the scope of the claims.

1. A mixer comprises: reference current source operably coupled toproduce a reference current; programmable gain radio frequency (RF)transconductance section operably coupled to convert an RF voltage intoan RF current based on a gain setting signal and the reference current;and switching quad transistors operably coupled to receive the RFcurrent and a local oscillator voltage, wherein the switching quadtransistors produce a frequency translated current.
 2. The mixer ofclaim 1 further comprises: current source pair operably coupled toprovide DC current to the switching quad transistors; common modecircuit operably coupled to provide a common mode voltage to the currentsource pair based on a common mode reference; and resistor sectionoperably coupled to switching quad transistors and to the current sourcepair to produce the common mode reference and to convert the frequencytranslated current into a frequency translated voltage.
 3. The mixer ofclaim 1 further comprises: current source pair operably coupled toprovide DC current to the switching quad transistors; common modecircuit operably coupled to provide a common mode voltage based on acommon mode reference, wherein the common mode circuit includes:resistive divider operably coupled to the switching quad transistors,wherein a tap of the resistive divider provides the common modereference; operational amplifier having inputs operably coupled to areference voltage and to receive the common mode reference; transistorpair operably driven by an output of the operational amplifier; andresistor pair operably coupled to the transistor pair to provide anoutput of the mixer.
 4. The mixer of claim 1 further comprises: currentsource pair operably coupled to provide DC current to the switching quadtransistors; common mode circuit operably coupled to provide a commonmode voltage based on a common mode reference, wherein the common modecircuit includes: resistive divider operably coupled to the switchingquad transistors, wherein a tap of the resistive divider provides thecommon mode reference; second resistive divider operably coupled to thetap of the resistive divider to provide a scaled representation of thecommon mode reference; operational amplifier having inputs operablycoupled to a reference voltage and to receive the scaled representationof the common mode reference; transistor pair operably driven by anoutput of the operational amplifier; and resistor pair operably coupledto the transistor pair to provide an output of the mixer.
 5. The mixerof claim 1 further comprises: resistor section operably coupled toconvert the frequency translated current into a frequency translatedvoltage.
 6. The mixer of claim 1, wherein the programmable gain RFtransconductance section further comprises: RF input transistor pairoperably coupled to receive the RF signal; first tapped inductoroperably coupled to the RF input transistor pair; second tapped inductoroperably coupled to the RF input transistor pair; and selectabletransistor section operably coupled to the first and second tappedinductors and to the reference current source, wherein, based a firststate of the gain setting signal, the selectable transistor sectioncouples the first and second tapped inductors to the reference currentsource to provide a first gain, and wherein, based on a second state ofthe gain setting signal, the selectable transistor section couples thefirst and second tapped inductors to the reference current source toprovide a second gain.
 7. The mixer of claim 1, wherein the programmablegain RF transconductance section further comprises: RF input transistorpair operably coupled to receive the RF signal; differential tappedinductor operably coupled to the RF input transistor pair; andselectable transistor section operably coupled to the differentialtapped inductor and to the reference current source, wherein, based afirst state of the gain setting signal, the selectable transistorsection couples the differential tapped inductor to the referencecurrent source to provide a first gain, and wherein, based on a secondstate of the gain setting signal, the selectable transistor sectioncouples the differential tapped inductors to the reference currentsource to provide a second gain.
 8. The mixer of claim 1, wherein theswitching quad transistors further comprises: native transistorsoperably coupled to produce the frequency translated current such thatflicker noise of the mixer is reduced and gate to body voltage of theswitching quad transistors is reduced.
 9. An intermediate frequency (IF)module comprises: local oscillator operably coupled to provide a localoscillation voltage; first mixer operably coupled to mix an in-phasecomponent of a signal with an in-phase component of the localoscillation voltage to produce an in-phase product; second mixeroperably coupled to mix a quadrature component of the signal with aquadrature component of the local oscillation voltage to produce aquadrature product, wherein each of the first and second mixersincludes: reference current source operably coupled to produce areference current; programmable gain radio frequency (RF)transconductance section operably coupled to convert voltage of thesignal into current of the signal based on a gain setting signal and thereference current; and switching quad transistors operably coupled toreceive the current of the signal and the local oscillator voltage,wherein the switching quad transistors translate frequency of thecurrent of the signal to produce the in-phase product and the quadratureproduct, respectively; summing module operably coupled to sum thein-phase product and the quadrature product to produce a summed signal;and filter module operably coupled to filter the summed signal toproduce an IF signal.
 10. The IF module of claim 9, wherein each of thefirst and second mixers further comprises: current source pair operablycoupled to provide DC current to the switching quad transistors; commonmode circuit operably coupled to provide a common mode voltage to thecurrent source pair based on a common mode reference; and resistorsection operably coupled to switching quad transistors and to thecurrent source pair to produce the common mode reference and to convertthe frequency translated current into a frequency translated voltage.11. The IF module of claim 9, wherein each of the first and secondmixers further comprises: resistor section operably coupled to convertthe frequency translated current into a frequency translated voltage.12. The IF module of claim 9, wherein the programmable gain RFtransconductance section further comprises: RF input transistor pairoperably coupled to receive the RF signal; first tapped inductoroperably coupled to the RF input transistor pair; second tapped inductoroperably coupled to the RF input transistor pair; and selectabletransistor section operably coupled to the first and second tappedinductors and to the reference current source, wherein, based a firststate of the gain setting signal, the selectable transistor sectioncouples the first and second tapped inductors to the reference currentsource to provide a first gain, and wherein, based on a second state ofthe gain setting signal, the selectable transistor section couples thefirst and second tapped inductors to the reference current source toprovide a second gain.
 13. The IF module of claim 9, wherein theprogrammable gain RF transconductance section further comprises: RFinput transistor pair operably coupled to receive the RF signal;differential tapped inductor operably coupled to the RF input transistorpair; and selectable transistor section operably coupled to thedifferential tapped inductor and to the reference current source,wherein, based a first state of the gain setting signal, the selectabletransistor section couples the differential tapped inductor to thereference current source to provide a first gain, and wherein, based ona second state of the gain setting signal, the selectable transistorsection couples the differential tapped inductors to the referencecurrent source to provide a second gain.
 14. The IF module of claim 9,wherein the switching quad transistors further comprises: nativetransistors operably coupled to produce the frequency translated currentsuch that flicker noise of the mixer is reduced and gate to body voltageof the switching quad transistors is reduced.